The invention relates to a process for chip removing machining of bore surfaces that are spaced at a distance from one another in axial direction, particularly of crankshaft and/or camshaft bearing bores, in accordance with Claim 1.
For the machining of bore surfaces of the type addressed here, particularly crankshaft and/or camshaft bearing bores, a long boring bar is used, which is inserted into the bore to be machined. The boring bar is guided with the aid of guide bushes, which are positioned very precisely in relation to each other and are arranged in front of the first bore surface or after the last bore surface as viewed in the feed direction of the boring bar. Frequently, an additional guide bush disposed in the area between the two outermost bore surfaces is used. This guidance of the boring bar is to ensure that the bores are in alignment with one another, i.e., that they are precisely radially aligned in relation to one another, which is crucial particularly in crankshaft/camshaft bearing bores for the performance of the engine. It has been shown, however, that in the known processes for the machining of bore surfaces, the mean position of the bore center does not always meet these requirements.
Thus, it is the object of the invention to define a process for machining bore surfaces that are spaced at a distance from one another in axial direction, which will ensure a high alignment accuracy of the bores.
To attain this object, a process with the features of Claim 1 is proposed. This process is distinguished in that the surface of at least one of the two outermost bores is machined first to produce a bearing surface for machining additional bore surfaces. Finally, a boring bar is inserted through one of the machined outermost bores into at least one of the bores lying between the outermost bore surfaces. To machine the bore surfaces, the boring bar comprising at least one cutting device is set into rotation and displaced in axial direction. Since the boring bar is guided within at least one of the two outermost bore surfaces that have already been finished, a high alignment accuracy of the bores can be ensured.
A particularly preferred embodiment of the process provides that both outermost bore surfaces be machined. The boring bar is preferably inserted into all the bores, i.e., into the two outermost bores previously machined for the purpose of supporting the boring bar as well as into the bores arranged therebetween. The two outermost bore surfaces that serve as the bearing surfaces or bearings center the boring bar. Subsequently the remaining bores are machined by at least one cutting device through a rotary and translatory motion of the boring bar. Centering the boring bar makes it possible to realize a very precise mean position of the bore center. In other words, a high alignment accuracy of the bores is ensured.
An advantageous embodiment provides that one of the outermost bore surfaces is machined first and the workpiece with the bore surfaces, for example a crankshaft housing, is then pivoted 180xc2x0 about an axis into a second machining position in which the other outermost bore surface can be machined. This procedure makes it possible to machine the two outermost bore surfaces using the same tool without having to shift the tool into a different working position. The pivoting axis preferably extends in vertical direction, i.e., radially to the longitudinal center axis of the bores.
A further development of the invention provides that the boring bar is inserted through one of the machined bores and an opposite tool is inserted through the opposite outermost bore and that the two are coupled together. According to a first variant it is provided that the outside diameter of the opposite tool is adapted to the diameter of the outermost machined bore in such a way that the opposite tool is very precisely centered or guided through the bore. According to a second variant it is provided that the outside diameter of the opposite tool is smaller than the diameter of the outermost machined bore and that the opposite tool comprises a guide element with several guide bars distributed over the circumference of the opposite tool and spaced at a distance from one another. The guide bars are designed so that they can be retracted into and extended from the opposite tool. Before or after the opposite tool is inserted into the bore, the guide bars are changed from a retracted to an extended position in which they are supported against the bore surface to guide and center the opposite tool within the bore. In both these variants, the boring bar is centered and guided by suitable means within the opposite outermost machined bore.
The coupling of the boring bar and the opposite tool can be rotationally fixed in such a way that if a driving or braking torque is applied to the boring bar, the opposite tool is carried along, or if a torque is applied to the opposite tool, the boring bar is carried along, so that the opposite tool or the boring bar also rotates. Hence, the coupling can be effected in such a way that if the boring bar is shifted in the direction of its longitudinal axis, the opposite tool is also shifted back and forth.
Of course, the connection between boring bar and opposite tool can also be designed in such a way that the two parts are exclusively centered in relation to each other, so that the opposite tool is not carried along if the boring bar is rotated and possibly shifted in axial direction. In this case, the opposite tool remains stationary as the bore surface is machined.
A further embodiment of the process is distinguished in that a guide sleeve is used as the opposite tool, which is coupled with the front end of the boring barxe2x80x94as seen in insertion direction of the boring barxe2x80x94after the boring bar has been inserted into the bore. This coupling is preferably effected by pushing the front end of the boring bar into the guide sleeve arranged in the outermost bore or by pushing the guide sleeve onto the front end of the boring bar. The front end of the boring bar is freely movable within the guide sleeve in axial and circumferential direction. The guide sleeve is designed in such a way that in its mounted state it reaches at least into the outermost machined bore, or reaches completely through it.
Furthermore, in an additional embodiment of the process, it is provided that the boring bar is eccentrically inserted into the bores. For this purpose, e.g., the boring bar is lowered or raised, e.g., by 2 mm to 3 mm, while the component with the bore surfaces to be machined, e.g., a cylinder block or camshaft housing, is kept stationary in a fixed position. After the boring bar has been inserted into the bore, it is raised or lowered again, set into rotation, and moved in axial direction in order to machine the bore surfaces. In this embodiment, the at least one cutting device can be fixedly mounted to the boring bar. It is also possible, however, that the at least one cutter of the cutting device is designed to be retracted into and extended from the boring bar. If a boring bar with radially displaceable cutters is used, an eccentric insertion of the boring bar into the bores may possibly be dispensed with, i.e., the boring bar, which has a smaller diameter than the bore surfaces to be machined, is brought into a position in which it is aligned with the two outermost machined bores and is then inserted into the bores. Another embodiment of the process provides that the workpiece with the bores is raised or lowered for the eccentric insertion of the boring bar into the bores, and that only after the boring bar has been inserted into the bores, the workpiece is raised or lowered again to a sufficient extent that the longitudinal center (rotary) axis of the boring bar is aligned with the longitudinal center axis of the bores. In this case the boring bar is in a fixed position, at least while it is being inserted into the bores.
Also preferred is an embodiment of the process in which the remaining bore surfaces that are arranged between the outermost bores are machined simultaneously. The boring bar comprises a respective cutting device for the bore surfaces arranged between the outermost bore surfaces, so that all the bore surfaces between the outermost machined bore surfaces are machined simultaneously as the boring bar rotates about its longitudinal axis and is displaced in the direction of its longitudinal axis. This makes it possible to reduce the boring bar machining time. With this simultaneous machining of all the bores and possibly an offset arrangement of the cutting devicexe2x80x94as seen in circumferential direction of the boring barxe2x80x94a balance of the forces can be achieved.
In another embodiment of the boring bar, the boring bar is provided with only one cutting device for all the bore surfaces to be machined. With this boring bar, the bores arranged in series are machined successively.
Finally, another embodiment of the process is preferred, which is distinguished in that the bore openings are provided with first and second chamfers through a back or forth movement of the boring bar in the direction of its longitudinal axis. Chamfering of the bore openings can be done before or after the bore surface is machined. For this purpose, the boring bar has at least one, preferably several cutters respectively assigned to a bore surface, which can be displaced in radial direction beyond the bore surface. Preferably, the same cutting device is used to machine the bore surface and to chamfer the openings of the bore.
Additional advantageous embodiments of the process are set forth in the other dependent claims.
Below, the invention will now be described in greater detail by means of the drawings in which:
FIG. 1 is a longitudinal section through a first embodiment of a boring bar:
FIG. 2 is a longitudinal section through a second embodiment of the boring bar;
FIG. 3 is a detail of a further embodiment of the boring bar;
FIG. 4 is a longitudinal section through a fifth embodiment of the boring bar;
FIG. 5 is a longitudinal section through the boring bar of FIG. 4 with the workpiece rotated 180 degrees;
FIG. 6 is a longitudinal section through a sixth embodiment of the boring bar; and
FIG. 7 is a partial longitudinal section through the boring bar of FIG. 6.